Isao Matsuzaki

A highly active and highly selective oxide catalyst for the conversion of ethanol to acetone in the presence of water vapour

In the presence of water vapour and a suitable catalyst, ethanol is converted to acetone rather than to ethylene and acetaldehyde. In order to develop an appropriate catalyst for this reaction, steady-state catalytic activities and selectivities were studied for 24 oxide catalysts. It was found that the acetone selectivity is high on a catalyst having both surface acidity and basicity, suggesting that the acetone formation is an acid-base bifunctional catalytic reaction. Iron oxide is superior to the other oxides studied here in both conversion and acetone selectivity. The superiority is greatly enhanced by mixing iron oxide with zinc oxide. The preparation method for the iron–zinc mixed oxide catalyst was also studied and it was found that the optimal composition is Zn/(Fe + Zn)= 0.1–0.4 and that the optimal condition for calcination is 773 K for 3 h. The catalyst gave 100% ethanol conversion and 94% acetone selectivity at a reaction temperature of 713 K. It is initially a mixture of Fe2O3 and ZnO but is converted to a spinel type compound, ZnFe2O4, during the reaction. The optimal reaction temperature was determined to be 713 K, and at this temperature, the acetone yield decreased by 34% after a time of 24 h.

Relation between the formation constant and the local structure of various bases and reference acids for the 1 : 1 hydrogen-bond complexation in aprotic solvents

For the 1 : 1 hydrogen-bond complexation of various bases against reference acids in aprotic solvents, the formation constant has been correlated with the local structure of acids and bases by regarding a base or an acid as composed of two local structural units, a functional group and a residual moiety. The following equation has been introduced to correlate log K, where K is the formation constant with the local structures: log K=(ηy+ηx)ωbωa+ log K0 where ηy and ηx represent the nature of the functional group of the base and acid, respectively, ωb and ωa represent the electronic effects of the residual moiety of the base and acid, respectively, and log K0 is a constant.Family-independent and -dependent behaviour observed for log K of 26 bases against p-fluorophenol, phenol and 5-fluoroindole in CCl4 are reasonably interpreted by applying the above equation. Formal ωb values of the bases have been evaluated. It has been pointed out that Maria–Gals angle θ which represents the electrostatic: covalent ratio of hydrogen bonding reflects the nature of the functional group of reference acids, as well as ηx.

Mechanism of the oscillatory decomposition of hydrogen peroxide in the presence of iodate ion, iodine etc.

Various mechanisms are constructed with the aid of information on associated reactions and tested in the light of the theory of two-variable oscillating reactions as well as by means of computer simulations. Reactions were run mainly at [HClO4]0= 0.035 to 0.080, [KIO3]0= 0.40, and [H2O2]0= 0.30 mol l.–1 and compared with computer results for a promising mechanism. Agreement is so good with respect to the induction period, the pulses of [I–] and the rate of O2 evolution, the abrupt decrease in [I2] etc. for one to conclude the mechanism to be plausible. The plausible mechanism contains HIO2, HIO, I–, H2I2O3, and H3I3O5 as intermediates and the second-order back-activation step 2HlO2+ HIO + H2O2→ 3HIO2+ H2O as the key step for the oscillation, which results from the sequence of HIO2+ HIO ⇌ H2I2O3, H2I2O3⇌ H3I3O5, and H3I3O5+ H2O2→ 3HIO2+ H2O. The oscillation source of the mechanism has been found to be in conformity with the Brusselator.

Catalyst surface coverages of adsorbed species in the nickel-catalyzed ethylene hydrogenation

Abstract Three different views have been expressed about the degree to which the surface of nickel is covered by adsorbed species during the hydrogenation of ethylene: (1) coverage varies with reaction temperature and reactant pressures, (2) invariably full coverage, and (3) invariably negligible coverage. We have examined the validity of these views by the analysis of data obtained in 1934 and of recent data obtained by us. The 1934 data of Farkas, Farkas, and Rideal for pairs of successive runs of parahydrogen conversion and ethylene hydrogenation using parahydrogen were analyzed on the premise that conversion proceeds via the Bonhoeffer-Farkas mechanism and that hydrogenation proceeds via the associative mechanism. In the recent experiments, pairs of successive runs of equilibration and ethylene hydrogenation using protium and deuterium mixtures were made at 30 °, 80 °, and 150 °C and the data obtained were analyzed in a similar fashion. Our analysis indicates that surface coverage by adsorbed ethylene plus monoadsorbed ethane varies substantially with reaction temperature and reactant pressures.

Titration of H2SO4/SiO2-mounted catalysts in cyclohexane with pyridine based on a new acidity function considering the effect of physisorption sites

A spectroscopic and visual titration of H2SO4/SiO2-mounted catalysts in cyclohexane with pyridine has been carried out by applying a new acidity function S′A in which the strength and amounts of acid and physisorption sites are taken into consideration. The S′A function is defined by S′A= pβI+ pKP, I+ log([PI]/[AI]) for a surface on which a kind of acid site and a kind of physisorption site exist, where pβI is the basic strength of a Hammett indicator and KP, I represents the equilibrium constant of the indicator for physisorption; [PI] and [AI] are the amounts of the indicator adsorbed on physisorption and acid sites, respectively. The physical properties of silica gel used here as the carrier were estimated based on the adsorption isotherm of pyridine and several indicators. It was revealed through simulation of the base titration system based on the S′A function that the strength and amounts of physisorption sites influence the estimate of acid strength distribution by the titration method, and that existence of strong physisorption sites often makes the titration impossible. The results of the improved spectroscopic titration showed that acid sites equal to the amount of sulphuric acid exist on the mounted catalyst. The strength of these sites was estimated by analysing the obtained S′A curve and was expressed in terms of the equilibrium constant for pyridine adsorption. At the same time, the relative strength of several indicators on the catalyst was determined. From the results of the improved visual titration, it was revealed that acid sites that correspond to the amount of sulphuric acid exist on each of the three kinds of mounted catalyst. It was pointed out that the physical meaning of the strength and amount of acid sites obtained by the conventional method is very obscure.